Fermentation products, such as ethanol, are produced by first degrading starch-containing material into fermentable sugars by liquefaction and saccharification and then converting the sugars directly or indirectly into the desired fermentation product using a fermenting organism. Liquid fermentation products such as ethanol are recovered from the fermented mash (often referred to as “beer” or “beer mash”), e.g., by distillation, which separate the desired fermentation product from other liquids and/or solids. The remaining faction, referred to as “whole stillage”, is dewatered and separated into a solid and a liquid phase, e.g., by centrifugation. The solid phase is referred to as “wet cake” (or “wet grains” or “WDG”) and the liquid phase (supernatant) is referred to as “thin stillage”. Dewatered wet cake is dried to provide “Distillers Dried Grains” (DDG) used as nutrient in animal feed. Thin stillage is typically evaporated to provide condensate and syrup (or “thick stillage”) or may alternatively be recycled directly to the slurry tank as “backset”. Condensate may either be forwarded to a methanator before being discharged or may be recycled to the slurry tank. The syrup consisting mainly of limit dextrins and non-fermentable sugars may be blended into DDG or added to the wet cake before drying to produce DDGS (Distillers Dried Grain with Solubles).
Ethanol plants have struggled to maintain profitability, which is highly variable depending upon corn price, demand and price of DDGS, tax credits, gasoline consumption, ethanol exports, and changes to the Renewable Fuels Standard (RFS) mandates. New technologies for energy savings, higher yield of ethanol and higher value for co-products as well as various oil separation technologies contribute to the profitability of producing ethanol.
US patent application no. 2005/0079270 A1 discloses a method of dewatering corn stillage solids comprising adding to the solids an anionic copolymer comprising acrylic acid sodium salt, methacrylic acid sodium salt or 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt to form a mixture of water and coagulated and flocculated solids; and separating the water from the coagulated and flocculated solids using a dewatering device.
Dewatering of whole stillage is energy demanding and may consume up to one-third of the energy requirement of a plant producing ethanol or a similar fermentation product. Thus, there is a need for improving processes involved in dewatering of whole stillage.